The disclosures herein relate generally to orthopedic implants and more particularly to a tibial prosthetic implant having an adjustable stem.
A frequently acknowledged limitation related to stemmed tibia components is that they do not adequately address the medial anatomic location of the intramedullary canal. Presently known devices provide only a fixed amount of either anterior and/or medial offset. Problems presented to orthopedic surgeons regarding tibial prosthetic implants include centering a baseplate to preferably cover 85% of the proximal tibia. This is difficult because the tibia is not symmetrical and the intramedullary canal does not extend down the center of the tibia. Therefore, the stem component must be offset relative to the baseplate. This combination presents difficulties which have been dealt with in various ways.
U.S. Pat. Nos. 4,219,893 and 4,301,553 each disclose a prosthetic knee joint of the hinged type which permits rotation of the bones in two planes and has means for attaching the device to the bones as well as coupling means. The attaching means for the tibia is in the form of a flanged sleeve in which a flanged stem element is adapted to be rotatably received. The stem element and the attaching means for the femur are coupled together so that they are permitted to undergo relative rotation in the plane of flexion. The rotation of the stem in the sleeve about the axis of the shaft of the tibia permits rotational movement of the pair of bones in the axial plane. The stem is free to distract from the sleeve while maintaining alignment to insure proper reengagement. Bearing surfaces on the stem and sleeve elements are adapted to engage so that the large forces exerted on the implanted device by reason of the knee's function and mechanics are distributed over the substantial area of the congruent thrust bearing surfaces. Non-hinged knee joints with congruent bearing surfaces allow flexion and tibial rotation.
U.S. Pat. No. 4,624,673 discloses a two part system for fastening a dental prosthesis to the jaw bone having as a first part, an externally threaded thin wall sleeve which resides entirely within the jaw bone. The threads or other surface features are confined to the area near the point where the prosthesis enters the jaw bone. The sleeve has integrally, or accommodates, a non-threaded stem which extends relatively deeply into the jaw bone. The inner bore of the sleeve is a cone of a mechanically self locking taper. The second part, which extends outwardly from the jaw bone through the gum tissue, has a mating external taper which is driven within the sleeve to be locked therein. The second part supports an artificial tooth, bridge or other dental appliance. The concept also is applicable to a prosthetic device for any body joint.
In U.S. Pat. No. 4,634,444, an artificial joint having stepped convex and concave bearing surfaces is provided. The stepped configuration prevents the bearing surfaces from sliding past one another along their axis of rotating and thus stabilizes the joint against lateral dislocations. The stepped bearing surfaces faces may be employed in an artificial knee joint, and the joint is further stabilized against dislocations corresponding to the femur moving anteriorly with respect to the tibia.
In U.S. Pat. No. 4,846,839, a joint prosthesis component for implantation in the end of a bone is provided. The component comprises a collar which holds a stem in a fixed position. The envelope of the bone engaging surface of the collar has a shape and size which corresponds to the shape and size of the cancellous bone at the end of the bone in that the envelope of the collar is more ovoid than round, having a large diameter which lies medially to laterally and a smaller diameter which lies anteriorly to posteriorly when the component is implanted in the end of the bone. The collar, but not the stem, may be porous coated.
In U.S. Pat. Nos. 4,888,021 and 5,011,496, a prosthetic knee joint is provided having an extended position, an intermediate position, and a flexed position. The motion of the joining includes a minor segment from the extended positions to the intermediate position, and a major segment from the intermediate position to the flexed position. The center of pressure between the femoral component and the tibial component moves rearward on the tibia during the minor segment. During the major segment, the joint flexes about an axis of rotation with the bearing surfaces on the femoral and tibial components being in congruent engagement. The distal surface of the femoral component includes two rails for engagement with a patellar prosthesis. The contour of the rails is either a straight line or a concave curve to provide line contact between the rails and the patellar prosthesis. The patellar prosthesis may include a saddle-shaped surface so that the prosthesis and each of the rails can make contact over an area extending along the length of the rail.
In U.S. Pat. No. 5,271,737, a tibial prosthetic implant includes a base or base plate with an offset tibial stem. The base includes an inferior surface adapted to abut a resected surface of a patient's tibia and forms a base for articulating surfaces adapted to articulate with the patient's femoral condyles. The longitudinal center axis of the tibial stem extends from the inferior surface of the base and is offset from the center of the base. The offset places the stem in position to extend into the central canal of the tibia so that it does not substantially interfere with the cortical bone when the inferior surface of the base substantially abuts and aligns with the resected surface of the tibia.
Therefore, what is needed is a modular tibial component having the ability to medially and anteriorly offset the stem relative to the geometric centerline of the proximal tibial plateau, in varying amounts, based on a patient's anatomy and preferably be usable on either the right or left tibia to reduce the number of parts variations required to provide a suitable tibial prosthetic implant.